/*
 * Copyright (c) [2016] [ <ether.camp> ]
 * This file is part of the ethereumJ library.
 *
 * The ethereumJ library is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * The ethereumJ library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the ethereumJ library. If not, see <http://www.gnu.org/licenses/>.
 */

package com.filecoinj.crypto.jce;

import java.security.InvalidAlgorithmParameterException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.Provider;
import java.security.SecureRandom;
import java.security.spec.ECGenParameterSpec;

public final class ECKeyPairGenerator {

    public static final String ALGORITHM = "EC";
    public static final String CURVE_NAME = "secp256k1";

    private static final String algorithmAssertionMsg =
            "Assumed JRE supports EC key pair generation";

    private static final String keySpecAssertionMsg =
            "Assumed correct key spec statically";

    private static final ECGenParameterSpec SECP256K1_CURVE
            = new ECGenParameterSpec(CURVE_NAME);

    private ECKeyPairGenerator() {
    }

    public static KeyPair generateKeyPair() {
        return Holder.INSTANCE.generateKeyPair();
    }

    public static KeyPairGenerator getInstance(final String provider, final
    SecureRandom random) throws NoSuchProviderException {
        try {
            final KeyPairGenerator gen = KeyPairGenerator.getInstance
                    (ALGORITHM, provider);
            gen.initialize(SECP256K1_CURVE, random);
            return gen;
        } catch (NoSuchAlgorithmException ex) {
            throw new AssertionError(algorithmAssertionMsg, ex);
        } catch (InvalidAlgorithmParameterException ex) {
            throw new AssertionError(keySpecAssertionMsg, ex);
        }
    }

    public static KeyPairGenerator getInstance(final Provider provider, final
    SecureRandom random) {
        try {
            final KeyPairGenerator gen = KeyPairGenerator.getInstance
                    (ALGORITHM, provider);
            gen.initialize(SECP256K1_CURVE, random);
            return gen;
        } catch (NoSuchAlgorithmException ex) {
            throw new AssertionError(algorithmAssertionMsg, ex);
        } catch (InvalidAlgorithmParameterException ex) {
            throw new AssertionError(keySpecAssertionMsg, ex);
        }
    }

    private static class Holder {

        private static final KeyPairGenerator INSTANCE;

        static {
            try {
                INSTANCE = KeyPairGenerator.getInstance(ALGORITHM);
                INSTANCE.initialize(SECP256K1_CURVE);
            } catch (NoSuchAlgorithmException ex) {
                throw new AssertionError(algorithmAssertionMsg, ex);
            } catch (InvalidAlgorithmParameterException ex) {
                throw new AssertionError(keySpecAssertionMsg, ex);
            }
        }
    }
}
